I wouldn't think Nokia is entirely going to jump out of the phone OS biz, they've invested far too much in it.
I could see them dropping A platform though.
Symbian - Symbian is a freaking money sink based on those R&D articles that came out recently. Not to mention it's a sinking ship that they're only going to have to plug more and more holes on, and they go it alone with Symbian, having to reinvent the wheel for things already accomplish in other operating systems.
However, they have the one benefit of a large user base...but does it matter? Symbian wasn't really a constantly updating platform, the OS was locked to the phone, existing users lose nothing if Nokia stops developing it.
Meego - Tied very heavily to Intel's platform and hardware, which is currently at a competitive disadvantage in the market. Also, does the market really need 3 similar Linux platforms, Meego, Android, and WebOS? Android is the most developed and is well optimized for a variety of ARM processors, but Nokia would still have to strip most of it out to take advantage of their QT framework and their own services, leaving it to be little more than Meego. WebOS is a more stock Linux distribution, in line with Nokia's Meego, than Android, so it would make some sense to hitch their wagon to that, except would HP want to after spending so much on WebOS? Still, shared applications would be very easy to pull off.
On the plus side, any of the 3 mobile Linux distros would be cheap (far cheaper than Symbian) for Nokia to maintain. Intel is doing the bulk of the development on Meego, Google on Android, and HP on WebOS, and all 3 draw very heavily from the very active open source Linux world. Nokia's real baby is QT, the GUI toolkit that will run on all of these platforms anyway.
What I can't see: picking up stock Android or Windows Phone 7 as their operating systems. They compete too directly with too many of Nokia's services, and no way would Microsoft let someone modify their OS significantly. As for stock Android, is Nokia really ready to compete head to head with HTC et al as just another equipment manufacturer? They'd get eaten alive in the specsheet war and time to market.